Doug - Thanks for your remarks. The engine has 420 hours SMOH which
included a new camshaft, new bearings ect. I'm wondering if the main
issue (with the low compression) is that the 420 hours has been over 6
years (and the last year it hardly flew at all). IMHO the plane has not
been flown enough. Like I said I'm an no expert but wouldn't you think
that 70 hours a year is a little light on usage? Could this be the
cause of the low compression on the cylinder? Maybe and mabe not. I have
a mechanical background but it has been years since I turned a wrench
but if I remember about compression checks the procedure was to take a
reading and if it was low then you squirt oil into the low cylinder (wet
compression check)and if the reading came up then the rings were either
worn or sticking. This is because the oil would temporarily seal the
rings but do nothing to seal up the valves. If the reading stayed the
same then you would suspect a valve problem. Please don't flame me too
bad on this because it has ben a while since I've done any engine work.
Although I suspect I'll be doing some owner assisted things with
whatever plane I end up. :-)

Jon Kraus
PP-ASEL-IA
Student airplane purchaser


Doug wrote:

What is the TT on the engine, and what is the SMOH on the engine? If
either are high, you may be in for a total rebuild. ONE cylinder with
62 would concern me. If it's near TBO, you're probably in for a
rebuild. Typically as an engine ages, compression goes down and oil
usage goes up. Also check to see if the last rebuild included
crankshaft bearings, was it a total rebuild or just a top? Look for
oil in the front of the engine, this is evidence of main bearings
going out. A recently rebuilt engine can have cylinder replacements be
successful, but a good engine shouldn't need them. Like I said, if
it's near TBO, you're probably in for a rebuild, and if the last
rebuild wasn't a major, your probably going to have to major it. Its
not worth it to top a high time engine, IMO.

You haven't made a deal yet, so you can do whatever you want at this
point. Nothing wrong with buying knowing it will need a rebuild so
long as the buy price reflects this. You might get lucky and get 500
more hours, doing nothing.

If the compressions were all good, and no oil usage, you usually can
count on 500 more hours, REGARDLESS of the time on the engine.
Usually, not always. And nothing unusual about running it past TBO.
These Lycomings typically will run well past TBO.

Jon Kraus wrote in message . ..

My new partner and I are looking at a 1975 Mooney M20C. It is a nicely
upgraded IFR plane with a 400 hour O-360 engine. It is a rather high
time airplane (7000) hours and the price reflects this fact. It is being
sold by the owner of the FBO we fly out of for one of his friends. They
just finished up an annual inspection on it.

My IFR instructor has owned Mooneys in the past and even had the M20C
for years. He suggested that we fly the plane to Byerly Aviation in
Peoria IL (a little over an hour flight from Indianapolis) and have them
do the pre-buy. He said it would probably cost in the $500.00 range. My
partner and I think it is a good idea too. We are both buying our first
plane and think the money would be well spent.

One of the cylinders has a compression of 62 while the others are in the
70's. This concerns me even though it is within tolerances. Of course we
would hate to buy something that needed immediate major engine work. The
plane has not flown much for the past 2 years so I am wondering if after
flying the thing a while if the compression might come back some
(probably wishful thinking I know).

I am interested in opinions or experiences in first plane purchases.
Experience with Byerly Aviation. Or comments on the engine situation I
described. Thanks!!

Jon Kraus
PP-ASEL-IA
Student aircraft purchaser